President Donald Trump said on Monday the US will "begin cutting off" foreign aid to Guatemala, Honduras and El Salvador after he accused them of allowing people to leave the region and come "illegally" to the US in the migrant caravan.

However, cutting US aid may not be as easy as Trump thinks, according to experts, as Congress controls the U.S. purse strings, not the White House.

Trump cut U.S. aid to the Northern Triangle countries of Guatemala, Honduras and El Salvador by 30% in in his foreign aid budget requests for 2017 and 2018, but Congress reinstated most of the money, said Adam Isacson, who monitors U.S. aid to Latin America for the Washington Office on Latin America (WOLA), a Washington DC policy watchdog.

In 2017, Guatemala received over $177 million in U.S. aid. The same year, Honduras received $181 million and El Salvador $149 million, according to WOLA.

The Foreign Assistance Act limits the president's power of the purse and only allows him to transfer up to 10 percent between accounts, WOLA points out.A separate law, prohibits the president from withholding money that Congress has appropriated.

"If Congress gives aid it's because it thinks it's in the broad U.S. national interest. Donald Trump may in fact think this aid is suitcases of cash that goes to Central American leaders, but in fact it's all in kind, for training, equipment and services,” said Isacson.

His comments are widely seen as the latest attempt by Trump to revive a national conversation about immigration to fire up the Republican party base before the US mid-term elections.

The caravan of thousands is now making its way through Mexico towards the US.

"Shooting himself in the foot"

If the aid is cut Trump would be shooting himself in the foot as most of the aid goes to issues that Trump cares most about like border security, drug interdiction, and strengthening the police and military. “The idea is supposedly to protect people from some of the violence that is causing them to migrate,” said Isacson.

Central America has long been a source of migration due to civil wars in the 1970s and 80s, as well as political corruption, gang violence, natural disasters, including hurricanes and earthquakes, and endemic poverty. Over the last decade, U.S. policy has focused on reducing violence and increasing security in the Northern Triangle due to increased levels of migration. In 2008, the U.S. launched a $1 billion Central American Regional Security Initiative with a stated goal of advancing “community policing, gang prevention, and economic and social programming for at-risk youth and communities disproportionately affected by crime."

Alliance for Prosperity

This increased after a surge of child migrant at the U.S.-Mexico border in 2014. In response, the U.S. created another $700 million Plan for the Alliance for Prosperity in the Northern Triangle, the goal of which is "strengthening the region’s security, governance, and economic competitiveness, while also addressing the shared challenges of illegal immigration and trafficking."

The plan was passed by a Republican-controlled Congress with bipartisan support. Trump tried to cut funding for the Plan for Prosperity from $600 million to $400 million in 2018 and 2019, but Congress put back most of the funding.

Critics of U.S. policy have long argued that more money should be spent on social program to reduce poverty, rather than beefing up the police and military which are notoriously corrupt. “If Donald Trump wants to cut aid to the Honduran military we don’t have a dog in this fight,” said Isacson. “We don't think that aiding the military has been helped Honduras.”

But he pointed out that a large chunk of non-military aid is also designed to stop people from migrating, such as neighborhood violence reduction, justice reform and police training. “Most of this is what they would consider as 'hard-side' aid going to people in uniform directly, or other efforts to fight crime,” he added. “Only a little bit goes to digging wells for peasants.”